Properties of the complex between histone H1 and poly(ADP-ribose synthesised in HeLa cell nuclei

PARticular MARks: Histone ADP-ribosylation and the DNA damage response

Cellular and molecular responses to DNA damage are highly orchestrated and dynamic, acting to preserve the maintenance and integrity of the genome. Histone proteins bind DNA and organize the genome into chromatin. Post-translational modifications of histones have been shown to play an essential role in orchestrating the chromatin response to DNA damage by regulating the DNA damage response pathway. Among the histone modifications that contribute to this intricate network, histone ADP-ribosylation (ADPr) is emerging as a pivotal component of chromatin-based DNA damage response (DDR) pathways. In this review, we survey how histone ADPr is regulated to promote the DDR and how it impacts chromatin and other histone marks. Recent advancements have revealed histone ADPr effects on chromatin structure and the regulation of DNA repair factor recruitment to DNA lesions. Additionally, we highlight advancements in technology that have enabled the identification and functional validation of histone ADPr in cells and in response to DNA damage. Given the involvement of DNA damage and epigenetic regulation in human diseases including cancer, these findings have clinical implications for histone ADPr, which are also discussed. Overall, this review covers the involvement of histone ADPr in the DDR and highlights potential future investigations aimed at identifying mechanisms governed by histone ADPr that participate in the DDR, human diseases, and their treatments.

The Expanding Constellation of Histone Post-Translational Modifications in the Epigenetic Landscape

The emergence of a nucleosome-based chromatin structure accompanied the evolutionary transition from prokaryotes to eukaryotes. In this scenario, histones became the heart of the complex and precisely timed coordination between chromatin architecture and functions during adaptive responses to environmental influence by means of epigenetic mechanisms. Notably, such an epigenetic machinery involves an overwhelming number of post-translational modifications at multiple residues of core and linker histones. This review aims to comprehensively describe old and recent evidence in this exciting field of research. In particular, histone post-translational modification establishing/removal mechanisms, their genomic locations and implication in nucleosome dynamics and chromatin-based processes, as well as their harmonious combination and interdependence will be discussed.

ADP-ribosylation of histones by ARTD1: an additional module of the histone code?

ADP-ribosylation is a covalent post-translational protein modification catalyzed by ADP-ribosyltransferases and is involved in important processes such as cell cycle regulation, DNA damage response, replication or transcription. Histones are ADP-ribosylated by ADP-ribosyltransferase diphtheria toxin-like 1 at specific amino acid residues, in particular lysines, of the histones tails. Specific ADP-ribosyl hydrolases and poly-ADP-ribose glucohydrolases degrade the ADP-ribose polymers. The ADP-ribose modification is read by zinc finger motifs or macrodomains, which then regulate chromatin structure and transcription. Thus, histone ADP-ribosylation may be considered an additional component of the histone code.

Poly(ADP-ribosyl)ated chromatin domains: access granted

The seemingly static architecture of interphase and mitotic chromatin betrays an otherwise elegantly dynamic entity capable of remodelling itself to facilitate DNA replication, transcription, repair and recombination. Remodelling of local chromatin domains in response to physiological cues proceeds, at least in part, through transient cycles of relaxation and condensation that require use of histone variants and post-translational modifications of histones. Studies have connected poly(ADP-ribosyl)ation of histones with virtually every aspect of DNA metabolism and function over the years, most notably with the response to DNA damage, where convincing evidence supports its essential role granting repair machinery access to damaged DNA. Recent reports extend this notion to transcription and the maintenance of genomic stability, thereby supporting a general role for nuclear poly(ADP-ribosyl)ation in many aspects of genomic activity. The phenomenon might contribute to the 'histone code' by dictating levels of local chromatin compaction.

Histone variants and histone modifications: A structural perspective

In this review, we briefly analyze the current state of knowledge on histone variants and their posttranslational modifications. We place special emphasis on the description of the structural component(s) defining and determining their functional role. The information available indicates that this histone "variability" may operate at different levels: short-range "local" or long-range "global", with different functional implications. Recent work on this topic emphasizes an earlier notion that suggests that, in many instances, the functional response to histone variability is possibly the result of a synergistic structural effect.Key words: histone variants, posttranslational modifications, chromatin.

Dual inhibitory effects of dimethyl sulfoxide on poly(ADP-ribose) synthetase

Dimethyl sulfoxide (DMSO), a solvent popularly used for dissolving water-insoluble compounds, is a weak inhibitor of poly(ADP-ribose) synthetase, that is a nuclear enzyme producing (ADP-ribose)n from NAD+. The inhibitory mode and potency depend on the concentration of substrate, NAD+, as well as the temperature of the reaction; at micromolar concentrations of NAD+, the inhibition by DMSO is biphasic at 37 degrees C, but is monophasic and apparently competitive with NAD+ at 25 degrees C. DMSO, on the other hand, diminishes dose-dependently and markedly the inhibitory potency of benzamide and other inhibitors. Other organic solvents, ethanol and methanol, also show a biphasic effect on the synthetase activity at different concentrations.

Nuclear response of pancreatic islets to interleukin-1 beta

The mechanisms by which interleukin-1 (IL-1) exerts destructive action on the pancreatic islet beta-cells remain elusive. Fragmentation of DNA leading to the activation of poly(ADP-ribose) synthetase was investigated in the present study, by assessing the nuclear response to cytokines in rat pancreatic islets. Nuclear fractions display Mg(2+)-dependent poly(ADP-ribose) synthetase activity catalyzing the incorporation of [adenine-U-14C]NAD, with Ka and Km for Mg2+ and NAD amounting to 0.86 mM and 0.43 mM, respectively. Exposure of the nuclear fraction to rIL-1 beta (10 IU/ml) provoked DNA strand breaks and increased nuclear poly(ADP-ribose) synthetase activity (148.4%, P < 0.01). In intact islets, this nuclear response was observed after 18 h culture in medium containing rIL-1 beta, with a concomitant decrease in NAD (88.5%). Brief periods of pre-incubation (90 min) with rIL-1 beta were unable to induce any nuclear activity. Under these conditions, the presence of IFN-alpha (24 U/ml) and TNF (120 U/ml) was necessary to induce a response to rIL-1 beta. Under the latter experimental conditions, a decrease in NAD content was also observed. The nuclear effects of IL-1 beta were modified by nicotinamide (10 mM), an inhibitor of poly(ADP-ribose) synthetase. It is thus conceivable that an increase in poly(ADP-ribose) synthetase activity together with DNA break is implicated in the beta cytotoxic effect of interleukin-1 beta.

Characterization of a set of antibodies specific for three human histone H1 subtypes

A series of human histone H1 subtype-specific antibodies are described that were generated for localization and functional studies. Since our previous attempts to produce such antibodies against intact subtypes met with limited success, resulting in one antibody against a subtype we have designated H1-3, the approach used in the work presented is based on the production of antibodies against synthetic peptides or peptide fragments encompassing the variant NH2-terminal region of each protein. Subtype-specific antibodies were obtained against synthetic peptides derived from subtypes designated H1-1 and H1-2 and the NH2-terminal fragment from an N-bromosuccinimide digest of H1-4. Antibody specificities were documented in all cases by enzyme-linked immunosorbent and protein immunoblot assays against the purified subtypes as well as immunoblots against whole cell and nuclear extracts. In addition, the in vivo distribution of each antibody was determined by indirect immunofluorescence. H1-1 appears to be distributed in parallel with DNA concentration, similar to the results with an antibody that recognizes all subtypes. However, H1-2 and H1-4 are non-uniformly distributed, exhibiting similar punctate staining patterns. The staining patterns described are different from the pattern described for the distribution of H1-3, suggesting that several subtypes are concentrated in distinct regions of the nucleus and, therefore, may be associated with distinct regions of the genome.

Deletion mutants of poly(ADP-ribose) polymerase support a model of cyclic association and dissociation of enzyme from DNA ends during DNA repair

With an in vitro DNA repair system, Satoh and Lindah [(1992) Nature 356, 356-358] demonstrated that unmodified poly(ADP-ribose) polymerase (PADPRP) binds to radiation-damaged DNA and inhibits repair in the absence of NAD. However, in the presence of NAD, PADPRP undergoes automodification and the DNA is repaired. It was hypothesized that PADPRP cycles between an unmodified form, which protects DNA breaks, and an automodified form, which is released from DNA, thereby allowing access to repair enzymes. We have now tested this model with bacterially expressed mutants of PADPRP with deletions in the three major functional domains of the enzyme [Cherney, B. W., Chaudry, B., Bhatia, K., Butt, T. R., & Smulson, M. E. (1991) Biochemistry 30, 10420-10427]. Deletion mutants with an intact amino-terminal DNA-binding domain, and therefore capable of binding to DNA strand breaks in the in vitro assay, inhibited repair; however, whether the deletion was in the NAD-binding, active site domain or the automodification domain, the inhibition of repair exerted by these mutant proteins was not alleviated by NAD. A PADPRP mutant with a deletion in the DNA-binding domain did not inhibit DNA repair. Thus, the behavior of these PADPRP deletion mutants is consistent with the model proposed earlier. The model was also supported by experiments with Manley extracts of HeLa cells stably transfected with a PADPRP antisense RNA construct. Extracts of cells induced to express antisense RNA did not markedly inhibit in vitro DNA repair, nor did the addition of NAD influence the assay. In contrast, noninduced cell extracts inhibited repair and inhibition was alleviated by NAD.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Aminobenzamide inhibits poly(ADP ribose) synthetase activity and induces phosphoenolpyruvate carboxykinase (GTP) in H4IIE hepatoma cells

The purpose of this study was to determine whether changes in ADP-ribosylation affect expression of the gene encoding the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PEPCK) in H4IIE hepatoma cells. Treatment with 3-aminobenzamide, a specific inhibitor of poly(ADP ribose) synthetase, caused an 89% decrease of ADP-ribosylation in isolated nuclei, and resulted in a two- to threefold induction of immunoassayable PEPCK in cultured cells. In contrast, the structurally related compound p-aminobenzoic acid had no significant effect on either process. In vivo labeling of proteins with [35S]methionine, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography, showed that the induction of immunoreactive PEPCK by 3-aminobenzamide was due to a selective increase in the synthesis of the protein. The specific induction of PEPCK synthesis by 3-aminobenzamide was accounted for by a twofold increase of mRNAPEPCK which reached its maximal value 4 h after the addition of 3-aminobenzamide and returned to the basal level by 10 h. A possible role of ADP-ribosylation in cAMP or glucocorticoid induction of PEPCK was investigated in experiments in which H4IIE cells were treated with combinations of 3-aminobenzamide and either dexamethasone or a cAMP analog. In each case the effects on PEPCK induction were additive, indicating that glucocorticoids and cAMP induce PEPCK by pathways different from that used by 3-aminobenzamide.

In vivo characterization of the poly(ADP-ribosylation) of SV40 chromatin and large T antigen by immunofractionation

We have confirmed the poly(ADP-ribosylation) of large T antigen of SV40 by using antibodies to both large T antigen and poly(ADP-ribose) and consequently have begun to characterize how this post-translational nuclear modification of the viral protein modulates its biological functions. SV40 minichromosomal subpopulation containing replicative intermediate DNA was shown to have a significantly higher affinity for anti-poly(ADP-Rib)-Sepharose than viral chromatin fractions containing mature minichromosomal DNA. An anti-large T-Sepharose column was used to isolate T antigen from crude extracts by two different approaches: (1) large T antigen was labeled with [35S]methionine in vivo and the infected cell extract was immunofractionated to isolate large T antigen and (2) large T antigen from infected cell extracts was immunofractionated followed by immunostaining. Using these techniques, 1-10% of the total T antigen from infected cells was found to be poly(ADP-ribosylated). Minichromosome preparations per se were also subjected to immunofractionation on anti-large T-Sepharose. The high level of retention of poly(ADP-ribosylated) species of minichromosomes on this matrix suggested that this post-translational modification of viral chromatin may be related to those steps in viral replication and transcription under regulation by large T antigen.

Possible role of ADP-ribosylation of adenovirus core proteins in virus infection

We have investigated the role of poly(ADP)-ribosylation of adenoviral proteins in virus infection. Viral core proteins V and the precursor to protein VII were shown to be in vivo and in vitro acceptors of ADP-ribose. In vivo ADP-ribosylation was restricted to viral proteins as the histones were not labeled during the late phase of infection. The ADP-ribosylated core proteins were assembled into mature virus particles. In vitro ADP-ribosylation of adenoviral core proteins performed with purified poly(ADP-ribose) polymerase led to relaxation of the chromatin structure of both ts1 and wild type pyridine cores and pentonless particles and triggered the complete dissociation of wild type particles. A critical role for poly(ADP)-ribosylation in virus infection was confirmed by measuring the effect of the inhibitors 3-aminobenzamide and nicotinamide on virus particle yield and infectivity. Both inhibitors depressed particle yield by up to 9-fold, but infectivity was reduced by up to 10(4)-fold. These results suggest that ADP-ribosylation of adenovirus core proteins may have a role in virus decapsidation.

Histones and their modifications

Histones constitute the protein core around which DNA is coiled to form the basic structural unit of the chromosome known as the nucleosome. Because of the large amount of new histone needed during chromosome replication, the synthesis of histone and DNA is regulated in a complex manner. During RNA transcription and DNA replication, the basic nucleosomal structure as well as interactions between nucleosomes must be greatly altered to allow access to the appropriate enzymes and factors. The presence of extensive and varied post-translational modifications to the otherwise highly conserved histone primary sequences provides obvious opportunities for such structural alterations, but despite concentrated and sustained effort, causal connections between histone modifications and nucleosomal functions are not yet elucidated.

Physical studies by NMR and circular dichroism determining three structurally different domains in Physarum polycephalum histone H1

Combined studies which include, NMR spectroscopy, circular dichroism, amino acid analysis and polyacrylamide gel electrophoresis together show that the protein designated as histone H1 from Physarum polycephalum has many of the features of histone H1 derived from other sources. The molecular masses of the globular peptide and the whole molecule were found to be 9000 +/- 1000 Da and 33000 +/- 3000 Da respectively. NMR melting experiments showed that the half-melt temperature was 53 +/- 1 degree C and the enthalpy of melting was 100 kJ . mol-1. Unusual facets of the molecule are the relatively large numbers of histidine residues (6 or 7) and the mono, di and trimethylation of some of the lysines, the major type of modification being trimethylation of 9 +/- 2 residues. The conditions necessary for structuring Physarum H1 are not the same as the histone H1 from calf thymus. It is suggested that titration of the histidine residues is the most decisive step for the development of tertiary folding of the globular unit.

Nuclear chromatin condensation of mouse lymphoma (L-1210) cells by methylnitrosourea. An electron microscopic and biochemical study

When the mouse lymphoma (L-1210) cells are treated with methylnitrosourea (MNU) at 37 degrees C for 30 min and then cultured for 4 h in a normal medium nuclear structure and functions of the cells are changed. We have investigated the mechanism as to how nuclear structure and functions are changed by MNU. In MNU-treated cells euchromatin area diminishes and chromatin condensation occurs. [3H]thymidine and [3H]uridine uptakes of the MNU-treated cells decrease. In contrast, when the MNU-treated cells are cultured in the presence of 3-aminobenzamide, a specific inhibitor of poly(ADP-ribose) synthetase changes of nuclear structure do not appear. [3H]Thymidine and [3H]uridine uptakes are partially and almost completely recovered, respectively. Autoradiographs of the cells labelled with [3H]NAD, a substrate of poly(ADP-ribose) synthetase show that silver grains due to [3H]ADP-ribose are densely located only in the cells where chromatin condensation occurs. Chromatin-bound proteins of molecular masses 20-25 X 10(3) daltons are specifically poly(ADP-ribosyl)ated in the MNU-treated cells. These results suggest that MNU-induced chromatin condensation is caused by poly(ADP-ribosyl)ation of chromatinbound proteins.

Time course of polynucleosome relaxation and ADP-ribosylation. Correlation between relaxation and histone H1 hyper-ADP-ribosylation

Isolated rat pancreatic polynucleosomes were poly(ADP-ribosylated) with purified calf thymus poly(ADP-ribose) polymerase. A time course study was performed using an NAD concentration of 200 microM and changes in nucleosomal structure were investigated by means of electron microscopy visualization and sedimentation velocity determinations. In parallel, analyses of histone H1 poly(ADP-ribosylation) and determinations of DNA polymerase alpha activity on ADP-ribosylated polynucleosomes were done at different time intervals. A direct kinetic correlation between ADP-ribose incorporation, polynucleosome relaxation amd histone H1 hyper-ADP-ribosylation was established. In addition, DNA polymerase alpha activity was highly stimulated on ADP-ribosylated polynucleosomes as compared to control ones, suggesting increased accessibility of DNA to enzymatic action. Because of the strong evidence implicating histone H1 in the maintenance of higher-ordered chromatin structures, the present study may provide a basis for the interpretation of the involvement of the histone H1 ADP-ribosylation reaction in DNA rearrangements during DNA repair, replication or gene expression.

On the occurrence of polymers of H1, H1(0) and H5 in extracts of whole tissues. Artificial production during protein preparation

Inspection of preparations of H1, H1(0) and H5 histones made by extraction of whole tissues has shown that dimers and higher polymers of all three of these proteins are present. They may be formed by the cross-linking action of poly(ADP-ribose) chains which are linked to some of the protein molecules. Putative dimers and higher polymers were noted in preparations from various tissues and species. However, evidence is presented which suggests that production of these polymers is an artifact of precipitation during the preparation of the proteins, so the significance of the polymers is questionable.

Pyridine nucleotide synthesis in normal and neoplastic human pituitary cells in culture

14C-Nicotinic acid (NA) incorporation into nicotinamide adenine dinucleotide (NAD) was studied in cultures from 7 normal human pituitaries and 13 chromophobe adenomas. 14C-NA (7.2 microM) was incubated with both normal and tumor cell cultures for periods up to 48 hours. Cells and culture media were examined separately for metabolites at 24 and 48 hours. NAD was the major labeled metabolite found in both normal and tumor cells, accounting for 65.4% for normal cells and 56.8% for tumor cells of the total cellular label at 48 hours. Nicotinamide (NAm), a product arising from NAD, was the only labeled metabolite found in the culture medium, aside from the 14C-NA added initially. Total incorporation of 14C-NA into NAD was estimated by adding the cellular 14C-NAD and labeled products of NAD (NMN, NAm and NADP) to the 14C-NAm found in the medium for each culture. Cultures derived from adenomas demonstrated greater than twice the rate of incorporation of 14C-NA into NAD as did normal cell cultures (P less than 0.01 at 24 hours and less than 0.001 at 48 hours). This difference did not appear to be related to the secretory status of the tumor, since both secreting and nonsecreting tumors demonstrated increased rates when compared to normal cells. This difference also persisted in two different culture media and with cells that had been maintained in culture for different lengths of time (6-day dispersed cell cultures and 6- to 16-week fragment cultures).

Increased thermal stability of solubilized chromatin after poly(ADP-ribose) synthesis

A hyperthermic shift in the hyperchromicity curve of thermally denatured swine aortic-smooth-muscle-cell chromatin solubilized by digestion of nuclei with micrococcal nuclease was observed after the chromatin was incubated under conditions to allow poly-(ADP-ribose) synthesis by the endogenous poly(ADP-ribose) polymerase. When the order of solubilization and poly(ADP-ribosyl)ation was reversed, a smaller proportion of the solubilized chromatin exhibited greater thermal stability. Nuclease digestion of nuclei preincubated for poly(ADP-ribose) synthesis revealed no difference in kinetics of digestion or fragment size distribution compared to that of control nuclei. Poly(ADP-ribose) synthesis in these nuclei was proportionately greater in the chromatin fraction most resistant to solubilization by micrococcal nuclease treatment.

Simultaneous determination of linear and branched residues in poly(ADP-ribose)

Methodology for the routine and simultaneous determination of the linear and branched residues of poly(ADP-ribose) is described. The main features of the procedure consist of the isolation of poly(ADP-ribose) by affinity chromatography; enzymatic digestion of the polymer to the unique nucleosides ribosyladenosine and diribosyladenosine which are derived from linear and branched residues, respectively; formation of fluorescent derivatives of ribosyladenosine and diribosyladenosine; and identification and quantification of these compounds by high-pressure liquid chromatography coupled with fluorescence detection. A variation on the methodology which allows the detection and quantification of ribosyladenosine and diribosyladenosine without formation of their fluorescent derivatives is also presented. Analyses of several cell lines for their capacity to synthesize poly(ADP-ribose) with a branched structure showed that the proportion of branched sites was constant (0.7-0.8%) in each of the cell lines.

A note on the ADP-ribose-protein linkages in rat-liver nuclei: a possible approach to assessing megavitamin therapy with niacin

Nuclei isolated from rat liver were incubated with NAD whose two ribose moieties were respectively labeled with 3H or 14C. By enzymatic (phosphodiesterase) and/or chemical (hydroxylamine) attack on doubly labeled ADP-ribosylated nuclear residues, AMP was found after hydroxylaminolysis as well as iso-ADP-ribose after phosphodiesterase plus hydroxylamine, in the absence of detectable amounts of ribose-5-phosphate. This is taken to indicate the existence of additional ribose-protein binding sites in in vitro ADP-ribosylated nuclear proteins: Besides C-1" (Hayaishi et al., Stocken et al.) C-2' and/or C-3' (purine-near) as well as C-2" and/or C-3" (pyrimidine-near), not only at the end but also within the chain of oligo-ADPR.

Unique acceptors for poly(ADP-ribose) in resting, proliferating and DNA-damaged human lymphocytes

Acceptor proteins for poly(adenosine diphosphoribosyl)ation were determined in resting human lymphocytes, in lymphocytes with N-methyl-N'-nitro-N-nitrosoguanidine-induced DNA damage and in lymphocytes stimulated to proliferate by phytohemagglutinin. Kinetic studies showed that the increase in ADP-ribosylation which occurred in response to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) treatment was greater in magnitude but more transient in duration than that which occurred in phytohemagglutinin-stimulated cells. Gel electrophoretic analyses revealed that MNNG treatment and phytohemagglutinin stimulation both caused an increase in ADP-ribosylation of poly(ADP-ribose) polymerase and core histones. In MNNG-treated cells, an increase in ADP-ribosylation of histone H1 was also observed. In contrast, phytohemagglutinin-stimulated cells showed no increase in ADP-ribosylation of histone H1. In MNNG-treated cells there was also ADP-ribosylation of a protein of molecular weight 62 000, while in phytohemagglutinin-stimulated cells there was a marked increase in ADP-ribosylation of a protein of molecular weight 96 000. MNNG treatment of phytohemagglutinin-stimulated cells produced a pattern of ADP-ribosylation that appeared to be due to the combined effects of the individual treatments. 3-Aminobenzamide effectively inhibited ADP-ribosylation under all treatment conditions.

Relationship between histone H1 poly(adenosine diphosphate ribosylation) and histone H1 phosphorylation using anti-poly(adenosine diphosphate ribose) antibody

The chromatin-associated enzyme poly(ADP-Rib) polymerase catalyzes the posttranslational modification of histones. Antibody to poly(ADP-Rib) has been coupled to Sepharose, and the resultant immunoadsorbent was used to fractionate, specifically, histone H1 subpopulations undergoing this nuclear protein modification. When this method of separation was used, it was additionally observed that poly-(ADP-ribosylated) H1 species were highly accessible to in vitro phosphorylation by nuclear protein kinase. Phosphorylated H1 molecules were retained by the anti-poly(ADP-Rib)-Sepharose column due to the presence of endogenous poly-(ADP-Rib) components. Degradation of the latter moieties on phosphorylated H1 reversed their adsorption to the column.

Immunoaffinity fractionation of the poly(ADP-ribosyl)ated domains of chromatin

Antibody to poly(ADP-ribose) has been covalently coupled to Sepharose and utilized to isolate selectively oligonucleosomes undergoing the poly(ADP-ribosyl)ation reaction from the bulk of chromatin. Approximately 12% of the unfractionated oligonucleosomes were bound to the immunoaffinity column and these represented essentially 100% of the original poly(ADP-ribosyl)ated nucleosomal species in the unfractionated chromatin. Poly(ADP-ribosyl)ated chromatin was not bound by preimmune IgG columns. KSCN eluted the modified nucleosomes in the form of nucleoprotein complexes. The eluted chromatin components were shown to contain poly(ADP-ribosyl)ated histones as well as automodified poly(ADP-ribose) polymerase. By using [3H]lysine- and [3H]arginine-labeled chromatin, it was shown that the poly-(ADP-ribosyl)ated histones, attached to stretches of oligonucleosomes bound to the column, had a 6-fold enrichment of the modification compared to histones of the unfractionated chromatin. This indicated that non-poly(ADP-ribosyl)ated nucleosomes, connected and proximal to the modified regions, were copurified by this procedure. This allowed characterization of the oligonucleosomal DNA around poly(ADP-ribosyl)ated chromatin domains to be compared with the unbound bulk chromatin. The data indicated that immunofractionated poly(ADP-ribosyl)ated oligonucleosomal DNA contained significant amounts of internal single-strand breaks compared with bulk chromatin. The bound nucleo-protein complexes were found to be enzymatically active for poly(ADP-ribose) polymerase after elution from the antibody column. In contrast, the unbound nucleosomes, representing 90% of the unfractionated chromatin, were totally inactive in the poly(ADP-ribosyl)ation reaction.

Polyoma virus minichromosomes: poly ADP-ribosylation of associated chromatin proteins

The host nuclear enzyme poly(ADP-ribose) polymerase has been shown to be associated with the replicative intermediate and mature forms of polyoma virus minichromosomes. Minichromosome-associated histones H2A and H2B as well as several nonhistone proteins were poly ADP-ribosylated by endogenous poly(ADP-ribose) polymerase. In addition, minichromosome fractions catalyzed the formation in vitro of dimers of endogenous histone H1 linked by poly(ADP-ribose). Poly ADP-ribosylated polyoma virus minichromosome chromatin labeled in vivo with [3H]thymidine could be retained and eluted from anti-poly(ADP-ribose) immunoglobulin G-Sepharose. Pulse-labeled replicative intermediate minichromosomes were retained better on the antibody columns than were mature minichromosomes labeled for 2.5 h. The possible role of poly ADP-ribosylation of viral nucleosomes during polyoma replication or transcription is discussed.

ADP-ribosylation in permeable HeLa S3 cells

ADP-ribosylation in permeabilized metaphase and interphase cells using [32P]NAD at pH 8.0 have been compared. Incorporation into trichloroacetic acid insoluble material was 4-5-times greater in metaphase cells. 17-22% was in the soluble fraction which contained material released from the cells, 16-22% in the 0.2 M HCl extract (histones) of the cell ghosts and the remaining activity in the residual fraction. Fractions were analyzed using dodecylsulphate/polyacrylamide gel electrophoresis at pH 6.0. The soluble fractions from metaphase and interphase cells exhibited three common unidentified ADP-ribosylated proteins corresponding to 78 000, 54 000 and 36 000 Da. In addition metaphase cells contained several other ADP-ribosylated proteins not present in interphase cells. The 0.2 M HCl extracts gave from metaphase cells radioactivity in the 32 000-39 000-Da region suggesting ADP-ribosylation of histone H1 with up to 10 residues of ADP-ribose and in the 17 000-20 000-Da region indicating ADP-ribosylation of core histones. The pattern of ADP-ribosylation of core histone in metaphase and interphase cells was qualitatively similar whereas the number of ADP-ribose residues per H1 molecule was higher in metaphase cells. The residual fraction contained free poly(ADP-ribose) and oligo(ADP-ribose). The results do not lend support to a special function of ADP-ribosylated histones in the mitotic event while certain ADP-ribosylated non-histone proteins may be specific for metaphase cells.

Immunological evidence for the in vivo occurrence of a crosslinked complex of poly(ADP-ribosylated) histone H1

The poly(ADP-ribosylation) of histones, which occurs within a limited and functionally specific domain of chromatin, is a novel post-translational modification. However, in the past it has been difficult to study this process in living cells because the substrate of the reaction (NAD) does not permeate the plasma membrane. In the current study, antibodies specific for histone H1 and poly(ADP-ribose) were used to study the occurrence of poly(ADP-ribose)+ species of H1 in vivo. Perchloric acid-extracted proteins from synchronously growing HeLa cells were fractionated by electrophoresis and transferred to nitrocellulose, and the transferred moieties were allowed to react with the specific antibodies and then with 125I-labeled protein A. The results conclusively demonstrate the natural occurrence of poly(ADP-ribose)-crosslinked complexes of histone H1 (i.e., H1 dimer), at the S/G2 phase transition of the cell cycle.

3T3-L1 preadipocyte differentiation and poly(ADP-ribose) synthetase

Differentiation of 3T3-L1 preadipocytes, induced by methyl-isobutylxanthine (MIX), dexamethasone (DEX), and insulin, results in cells with the morphological and biochemical characteristics of adipocytes. Following incubation of 3T3-L1 cells with MIX, DEX, and insulin, poly(ADP-ribose) synthetase activity decreased abruptly, remained low for several hours and then increased; this rise was delayed by readdition of MIX, DEX, and insulin. The transient reduction in poly(ADP-ribose) synthetase activity in 3T3-L1 cells occurred prior to the appearance of the adipocyte phenotype induced by the above agents. It was not observed when preparations were assayed in the presence of DNase I, indicating that poly(ADP-ribose) synthetase activity was masked following treatment with MIX, DEX, and insulin. The change in synthetase activity represents the earliest alteration of a specific enzyme yet detected during the differentiation of 3T3-L1 cells. It appears to be differentiation specific since nondifferentiating 3T3-C2 control cells did not exhibit changes in poly(ADP-ribose) synthetase activity when treated with MIX, DEX, and insulin. The transient reduction in activity may be an early event in differentiation which reflects changes in chromatin structure.